The present invention relates to an improved, gear mechanism for controlling the motion and angular displacement of upper and lower members of a leg brace for the stabilization and control of a human knee joint of the left and or the right leg, and more particularly to a pair of intermeshing perpendicular elliptical gears, one invading and the other retreating, and including structure for limiting the angular displacement of the gear.
The prior art describes many orthopedic devices which attempt to support and stabilize the human knee over a wide range of angular, lateral and rotational displacement of the human leg. However, in most cases high integration of a motion controlling structure produces a non-smooth operation. In U.S. Pat. No. 4,773,404 to Jeffrey H. Townsend one of the hinge members is required to snap sharply in one direction before pivoting can take place. This is also described in U.S. Pat. No. 5,330,418 to Jeffrey H. Townsend. In U.S. Pat. No. 4,940,044 to Castillo, the hinge is placed so far forward of the axis of pivot of the leg that the device does little more than tenuously accommodate a pivot connection between the upper and lower cuff members.
In all of these cases, a smooth control between the upper and lower cuffs of a leg brace is simply not obtainable. The use of two circular gears alone would not provide a movement which is more supportive to the leg joint throughout its angular displacement. A simple single or double circular gear cannot produce a motion which closely follows the arc of rotation of the human knee which is based upon the cam shaped condyles of the human femur. This cam shape is commonly referred to as the sagittal plane in the orthopedic profession and commonly varies only slightly from person to person. This movement path is generally described as being of a lesser radius or flatter curve at the initiation of movement and thence transitioning into an increasingly tighter, yet relatively constant radius motion. The above described hinges are clumsy attempts to provide a hinge which provides a shifting radius throughout the angular displacement of the hinge to truly track the motion of the human knee.
Another drawback of the hinges, such as those referred to above is the use of pins traveling in slots. These devices create additional friction through extended friction surfaces and concentrate the force in the pins sliding in the slots.
Another problem with currently available hinges is their width profile. Most two component hinges have overlapping members supported from one side, or have mutual support between the overlapping members. The width is bulky and the extension, even when not in flexion, is such that it must be worn with looser clothing. In flexion, the protrusion in the direction toward the front of the knee is severe and even more space and looser clothing is required. In addition, forward extension during flexion increases the probability that the brace will be caught or snagged on other objects, or as clothing is damaged from being stretched across the protruding hinge.
What is therefore needed is a hinge which enables guided controlled movement support of the knee, which is as friction free as possible. The needed hinge should be able to bear significant weight without binding and should produce a motion which is as close as possible to the movement of the human leg and which eliminates pin in slot structures.
The brace hinge of the present invention includes an upper and lower intermeshing gear members each having an elliptical gear intermeshed with the other and sandwiched by two very thin profile cover and support plates. The elliptical gears produce an eccentric motion which lends it self to following the natural motion of the human knee or other joints such as the elbow other motion of other joints can be mimicked as needed by varying the shape of the ellipses of the gears used in the hinges and further utilizing an ellipse which actually increases desirable forces during the motion of the hinge to increase the performance of the brace. The user""s knee, or other joint, will track in a correct natural arc and will be controlled by the brace having the hinges of the invention applying controlling forces to the knee or other joint to prevent its deviation from its correct and natural path.
The elliptical gear of one member has its radius extend toward the pivot axis of the other gear as the radius of the other elliptical gear retreats from the pivot axis of the one member. The magnitude and radial extent over which the ellipse extends can be varied. The combination of advancing and retreating radius gear members, relatively few gear teeth and sandwiched support plates eliminate any interruption to a smooth transition, provide superior load bearing ability and provide for extremely low friction. Because of the planar and close fitting of the surfaces between the cover and support plates and the upper and lower gear supports the hinge can hold lubrication for an extended period. The hinge members can be constructed of plastic, ceramic, metal, metal matrix composite or any combination thereof. The mesh points of the gear teeth provide a constant force there between along a line drawn from one rotational or pivot center to the other. The ellipses reciprocally compensate and they gain and withdraw the mesh interface moves from one gear support pivot point to the other.
The elliptical advancing and retreating interface is protected and stabilized by support and stabilization plates. The specific characteristics of the elliptical gears can be custom formed by the user or technician to even more closely follow the leg angular displacement motion and knee characteristics of a given user. Although the embodiment herein illustrates a 0xc2x0 to 180xc2x0 angular displacement of the hinge, other displacement ranges can be provided.
The cover and support plates form a seemingly center link and retract through flexion relative to the farthest forward point of the knee when viewed from the side. This creates a slimmer profile for the brace at the hinge level when viewed in the horizontal plane.